With the advent of a new as well as continuing pressures for improved environmental conditions in manufacturing and production facilities, lighting levels in those facilities have become of increasing importance. In addition, energy conservaion considerations have made it apparent that the use of high pressure mercury and sodium vapor light sources provide the best solution to both of these problems. The energy conservation considerations go beyond merely the manufacturing and production facilities and extend into commercial applications such as supermarkets and other retail outlets. The high pressure mercury or sodium vapor lamps can produce high illumination levels while consuming considerably less power. Although these light sources in the past have been used in manufacturing facilities in the form of high-bay luminaires of the industrial type, these fixtures left considerably to be desired in terms of esthetic appearance as well as the mounting heights at which they could be effectively employed. A need clearly exists for a high pressure mercury of sodium vapor luminaire for use in industrial and commercial applications wherein, in addition to having an esthetically pleasing appearance, a high beam spread can be provided to permit significantly lower mounting heights for the luminaire. Of course, beam spreading prisms can be employed in connection with a luminaire housing such as illustrated in design U.S. Pat. Nos. 205,411 and 229,090 or 179,339. One significant problem that these kinds of luminaires provide is at low mounting heights the user of the illumination is subjected to a brightness effect caused by the significant contrast between the transparent prismatic refractor and the totally opaque luminaire housing. The subconscious effect of this contrast in terms of the apparent brightness of the luminaire provides a comparatively unsatisfactory environment for those persons who must work or shop under these conditions.